Clinton's campaign also released 10 years of returns from running mate Tim Kaine

Receive the latest national-international updates in your inbox

in this file photo, Democratic presidential candidate, former Secretary of State Hillary Clinton and her husband, former U.S. president Bill Clinton, appear at a campaign event on February 19, 2016 in Las Vegas, Nevada. The Clinton campaign released both Hillary Clinton's and Tim Kaine's tax returns on Friday.

Hillary and Bill Clinton earned $10.6 million last year, according to a tax filing released by her campaign Friday that sought to pressure presidential rival Donald Trump to disclose his tax returns.

The filing shows that the Clintons paid a federal tax rate of 34.2 percent in 2015. The bulk of their income — more than $6 million — came from speaking fees for appearances made largely before Hillary Clinton launched her campaign in April 2015. They gave more than $1 million to charity.

The release is part of an effort to undercut Trump's character by questioning the celebrity businessman's record. Trump has refused to make his filings public, saying they're under audit by the Internal Revenue Service and that he'll release them only once that review is complete. All major U.S. presidential candidates in modern history have released their returns.

The Clintons have disclosed returns for every year dating back to 1977, in part due to laws requiring public officials release returns. She put out her most recent eight years of tax filings last summer and several years during her first presidential bid.

Trump Booed Leaving New York Times

President Elect Donald Trump is booed as he walks through the lobby of The New York Times Building after a 75-minute meeting with Times journalists. The lobby of the Times building is open to the public, and a large crowd had gathered by the time he departed. (Published Tuesday, Nov. 22, 2016)

Seeking common ground with blue-collar workers who have been attracted to Trump's message, Clinton frequently mentions Trump's returns as a way of underscoring how his economic plans would benefit his personal interests and questioning whether he's as wealthy as he claims.

Democrats believe Trump's returns could be treasure trove of politically damaging information. They want to see his tax rate, charitable giving, and business dealings with foreign governments.

Trump Takes Meetings at His New Jersey Golf Club

President-elect Trump interviewed more than a dozen candidates for his administration at his New Jersey golf club over the weekend, including Mitt Romney, Rudy Guliani, Chris Christie and Kansas secretary of state Kris Kobach, who has been tough on immigration, and others. (Published Monday, Nov. 21, 2016)

The Trump campaign did not immediately respond to a request for comment.

Clinton's strategy is borrowed from President Barack Obama's winning playbook against Mitt Romney in 2012. Obama repeatedly used Romney's business dealings against him and seized upon the former Massachusetts governor's reluctance to release certain tax records.

Clinton's campaign also released 10 years of returns from running mate Tim Kaine and his wife, Anne Holton. Over the last decade, the couple has donated 7.5 percent of their income to charity, the campaign said, and paid an effective tax rate of 25.6 percent last year.

Kaine, the Virginia senator who's spent much of his life in public service, reported a far lower income than the Clintons. Over the past decade, he and his wife earned the most in 2014, more than $314,000 in adjusted gross income. The Clintons made about 90 times more, reporting nearly $28 million for the same year.

Clinton has tried to paint Trump has an out-of-touch business mogul but her substantial wealth has caused headaches. Republicans have seized upon the millions in speaking fees and a tone-deaf comment by Clinton in a 2014 interview that she was "dead broke" after leaving the White House in 2001. The couple owed millions in legal fees, but quickly generated far more from book deals, paid appearances and consulting fees.

In total, the Clintons earned than $139 million between 2007 and 2014, according to eight years of federal income tax returns released by her campaign last July.

The bulk of their income came from speeches delivered to corporate and interest groups, which paid Bill Clinton and later Hillary Clinton after she resigned as secretary of state in early 2013.

Bill Clinton's consulting work for GEMS Education, a global network of for-profit schools based in Dubai in the United Arab Emirates, earned him more than $5.6 million in fees between 2010 and 2015, according to the Clinton tax returns.

Trump Holds Series of Meetings With Potential Cabinet Candidates

President-elect Donald Trump is holding a series of meetings all weekend with potential candidates at his New Jersey golf course as he continues to mull over dozens of positions in his upcoming administration. NBC's Chris Pollone reports. (Published Saturday, Nov. 19, 2016)

Bill Clinton also earned more than $17 million over the same period for consulting work for Laureate Education, Inc., another worldwide for-profit education system based in Baltimore that has come under controversy.

Bill Clinton's office last year said he had ended his consulting relationship with Laureate, but no similar statement has been made regarding to GEMS, which stands for Global Education Management Systems. His office did not immediately respond to a question about whether he still has a relationship with GEMS.